Pancreatic FDG uptake on follow-up PET/CT in patients with cancer

To evaluate the breakdown of unexpected pancreatic ¹⁸F-fluorodeoxyglucose (FDG) uptake and the proportion of secondary primary pancreatic cancer on follow-up, patients with cancer underwent positron emission tomography/computed tomography (PET/CT). The participants consisted of 4,473 consecutive patients with cancer who underwent follow-up PET/CT between January 2015 and March 2019 at Kochi Medical School. Among the participants, 225 with a history of pancreatic cancer were excluded from the present study. Retrospective and blinded PET/CT evaluations of 4,248 patients were performed. In patients with pancreatic FDG uptake, the distribution of FDG uptake in the pancreas was evaluated. The final diagnosis was determined pathologically. A total of 14 (0.3%) of the 4,248 patients exhibited FDG uptake in the pancreatic area. Pancreatic abnormalities were detected in 14 patients, and included five cases of pancreatic metastases (36%), four cases of secondary primary pancreatic cancer (29%), two cases of lymph node metastases (14%), one case of malignant lymphoma (7%), one case of autoimmune pancreatitis (7%) and one case of pseudolesion (7%). One patient with early-stage secondary primary pancreatic cancer had a maximum standardized uptake value (SUV_max) <3.0. The remaining 13 patients had a SUV_max >3.0 in the pancreas. Of the 14 patients, two had multiple foci of FDG uptake in the pancreas. Patients with multiple foci of FDG uptake exhibited pancreatic metastasis from renal cell carcinoma and malignant lymphoma. In conclusion, the majority of patients with unexpected pancreatic FDG uptake on follow-up PET/CT exhibited malignancies; furthermore, ~30% of the malignancies detected in patients with pancreatic FDG uptake were secondary primary pancreatic cancers. In patients with unexpected pancreatic FDG uptake on follow-up PET/CT, primary cancer should be considered as well as metastatic tumors.